Gardeners who design their spaces with perennial flowers know the importance of keeping something in bloom at all times. Because flowers bloom at different times of the year, a well-designed garden full of perennials will always appear to be thriving. As one flower goes out of season, another comes into season, giving constant aesthetic appeal to a garden. Because of this, gardeners need to know which flowers bloom when, then design a scheme to keep the garden flourishing all year long.
According to the paragraph, what do gardeners need to know?
